The invention relates to switch and interrupter mechanisms, and more particularly to such mechanisms utilizing a gas such as sulfur hexafluoride (SF.sub.6) to extinguish an arc.
In such mechanisms, arc interruption is caused by the removal of heat, which is caused by gas flow over the arc. High currents require high gas pressure and density and the removal of large amounts of heat. Low currents require relatively low gas pressure and density and the removal of relatively small amounts of heat.
The required increase in gas pressure and density can be achieved in several ways. One way is to impart mechanical energy to a gas volume to compress the gas in a variable volume chamber and thereby provide the increased pressure and density. This is known as "puffer" interruption. A disadvantage of this method is that it requires a relatively large prime mover to provide the required energy needed for high currents. Another way to provide the required increase in pressure and density is to use the arc as a source of energy to raise the enthalpy of the gas. This is known as "suicide" interruption. A disadvantage of this method is that at low currents it provides insufficient energy for interruption. Furthermore, any given interrupter has a fixed volume that is sized to accommodate the maximum fault current anticipated. The interrupter is then relatively inefficient at other currents.
To improve poor low current performance, suicide interrupters have employed auxiliary means, e.g., secondary pistons and magnetic assists, to overcome the lack of gas flow. Such auxiliary means are relatively expensive and complex. Also, puffer interrupters and suicide interrupters have been combined in an effort to reduce the energy required from a prime mover when interrupting high currents. Such combined interrupters typically maximize the amount of gas which flows from the variable volume chamber by minimizing the remaining volume. While this utilizes all of the available gas, it is an inefficient use of suicide action. Also, current puffer interrupters avoid excessive gas temperatures by providing increased gas volume and flow. The increased volume provides additional gas to absorb heat, and the additional flow limits heat input to the gas. To accommodate the additional volume and flow, larger prime movers are required. A typical puffer interrupter causes a pressure rise on the order of 50-70 psi at no load or low current. The pressure rise at no load is solely the result of mechanical energy from the prime mover.